Pyrimidine nucleoside phosphorylase (PyNPase) and IL-1 alpha concentration were measured in colorectal cancer tissues from 15 patients who preoperatively administered 5'-DFUR orally. The relation between changes of the PyNPase activity and pathological effects of resected specimens was studied. PyNPase activity changes showed that the increase cases were 9 patients and the decrease cases were 6 patients in pre- and post-administration of 5'-DFUR. The IL-1 alpha concentration in cancer tissues was 2933.65 +/- 2038.65 in the decrease cases and 1207.51 +/- 1378.83 in the increase cases. The level was significantly higher in the decrease case (p < 0.05). And there tended to be more pathologically effective in the decrease cases than in increase cases. The effects of preoperative oral chemotherapy in colorectal cancer was strongly influenced by changes of PyNPase activity and IL-1 alpha concentration in tumor tissues.